Best way to reinstal Ubuntu?

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http://askubuntu.com – I have Ubuntu dual booting with Windows 7 on my laptop. Well, I ran into some issue with mounting the encrypted folders, and it just won't boot. I want to downgrade to 12.04 anyways. Whats the best way to uninstall 12.10 and install 12.04 in it's place? I have separate partitions for boot, root, swap, and home. Oh and I need to leave Windows intact. Thanks guys (HowTos)